1. Field of the Invention
The present invention relates to a test stream generating system for testing a digital television (DTV) receiver, and more particularly, to a DTV test stream generator which can prevent discontinuity phenomenon of a video and an audio at the time of repeatedly reproducing a test stream, a method thereof, and a test stream recording medium.
2. Description of the Related Art
Generally, in a digital broadcast system, all processes such as interactive operation, reproduction, compression, and etc. are performed by a digital signal unlike the conventional analogue broadcast system. According to this, the digital broadcasting system is a next-generation broadcasting technique in which a picture quality is clean and superior sound is obtained by subdividing a sound signal from a narrow compass to a wide compass.
In the conventional analogue television broadcasting system, one electric wave can carry only one image information, and sound information had to be sent by another electric wave. Contrary to this, in the digital broadcasting system, one electric wave can carry a plurality of image information and sound information, and information can be compressed without quality deterioration. Therefore, multi-channel can be set in a frequency band of the conventional analogue broadcasting channel. Also, information can be easily controlled by using a computer, and interactive characteristic to send information required by a viewer is possible. According to this, recently, the digital broadcasting system is fast applied and spread through various media such as ground wave, satellite, a cable television, and etc.
A DTV test has to be performed by receiving a signal from the digital broadcasting system. However, actually, the test is possible only in an operation test, and a test for special functions of the digital broadcasting receiver is not performed. Also, a special signal for a performance valuation of the digital broadcasting receiver is not provided. Therefore, a digital television receiver developer generally performs the DTV test by using a virtual broadcasting system for the function test and the performance valuation.
FIG. 1 is an exemplary view showing a notion of a DTV test using a virtual broadcasting system in accordance with the conventional art.
As shown in FIG. 1, for the DTV test using the virtual broadcasting system, a stream generator 101 generates a predetermined audio/video test stream for function test or performance valuation of the DTV receiver, a channel encoder 102 channel-encodes the test stream, a channel up converter 103 modulates and up-converts the channel-encoded test stream into a radio frequency (RF) level to output, a DTV receiver 104 (herein, a set-top box) receives the RF signal, and a measuring means 105 such as an oscilloscope or a display means 106 such as a high definition television/PC monitor (HDTV/PC) performs the function test and the performance valuation for the received test stream.
In the meantime, a length of the test stream required at the time of producing the DTV receiver has to be consecutive as a real broadcasting. Also, various kinds of test stream are required for the function test and the performance valuation of the DTV receiver. According to this, many channels and a large amount of data are generated.
However, a capacity of a computer storage medium which stores the DTV test stream is limited, so that a length of the limited test stream has to be minimized and repeated to reproduce. In the meantime, when the test stream of the limited length is repeated to reproduce, a reproduction time of video and audio elementary stream, ES, is hardly equalized with that of a transport stream, TS. Accordingly, when the test stream is repeatedly reproduced, discontinuity phenomenon of the video and audio is generated due to the disaccord between the TS and ES, so that a product tested in the DTV receiver production field may be misunderstood as an inferior one.
FIG. 2 is an exemplary view showing a discontinuity phenomenon generated when a DTV test stream is repeatedly reproduced.
Referring to FIG. 2, when the test stream ordered and sold for a quality test at the time of producing the DTV receiver is changed from a video frame to the TS, a relation among a video frame time, an audio frame time, and a video ES unit time and a TS packet unit time are shown. That is, a relation among a video frame 201, an audio frame and an audio ES 202, a video ES 203, and a TS packet 204 is shown. In FIG. 2, the discontinuity phenomenon generated when the DTV test stream is repeatedly reproduced results from a time difference tdiff between the ES and the TS, that is, a disaccord of a reproduction time, when the ES and the TS are repeatedly reproduced. Accordingly, if the program TS is repeatedly reproduced, the reproduction time difference tdiff is accumulated, so that the TS is not transmitted yet at a time point when a transmittance of the video/audio ES has to be completed. That is, since the TS is not transmitted at the time point when the video and audio have to be reproduced, the reproduction is impossible.
TABLE 1videoTransportdifference timerunningVideo ESstreambetween tves and tTStime tvftime tvestime tTStdiffStream name[sec][sec][sec][sec]np.ts37.637.59957737.60sm4.ts37.637.59957737.60sa.m2t.115.01515.03711115.040.025sa.m2t.1.new15.01514.97282514.9753280.039672TPhhi_bits.conf1.8401.8404241.8416480.001648Sample.trp1.3601.3329601.3987200.03872VIDn002b.12t4.04.0000873.999980.000018
The table 1 shows an analysis of a reproduction time for the transport stream provided in MPEG. Referring to the table 1, a difference among the video frame reproduction time, the ES reproduction time, the TS reproduction time is generated as tens of msec. The difference is generated when the ES is converted into the TS, because the TS is constituted as a packet unit. The time difference does not greatly influence in case of a non-repeated reproduction. However, in case of the repeated reproduction for the test, that is, in case of repeatedly reproducing the TS of a predetermined length, the discontinuity phenomenon of the video and audio is irregularly generated by the audio in a decoder, a size of a video ES buffer, an ES rate, a frame time, and etc. Accordingly, the discontinuity phenomenon generated due to the disaccord between the TS reproduction time and the ES reproduction time when the limited test stream is repeatedly reproduced influences on a reliability of the DTV receiver test.